Method of operating wax filters



Jan. 6, 1942. w.. E. WANNER ETAL METHOD OF OPERATING WAX FILTERS Filed Feb. 24, 1939 INVENTORS Patented Jan. 6, 1942 METHOD OF OPERATING WAX FILTERS Walter E. Wamier and David F. Renshaw, Olean, N. Y., assignors to Socony-Vacuum Oil Com pany, Incorporated, New York, N. Y., a corporation of New York Application February 24, 1939, Serial No. 258,204

v 4 Claims. (c1. Isa-19) This invention has to do with the operation of continuous rotary filters used in the separation of wax from a chilled slurry containing crystallized wax, oil, and a dewaxing solvent.

The so-called solvent dewaxing" process for the removal of wax from petroleum fractions comprises the steps of adding a solvent to the waxy oil, chilling the mixture to precipitate the wax therefrom, and separating the wax from the mixture by filtration.

The dewaxing solvent used may be a diluent to decrease the viscosity of the oil, or a material or mixture of materials in which the oil is substantially completely soluble and the wax substantially completely insolube at the selected dewaxing temperature, or a mixture of both. Embraced within the term sovent are light petroleum naphthas, liquefied normally gaseous hydrocarbons such as propane and its homologues, alcohols, ketones, aldehydes, benzol and its homologues, or other appropriate organic liquids. One solvent commonly so used is a mixture of benzol and methyl-ethyl ketone.

The operation of the continuous rotary filter normally used for separation of the precipitated wax may be understood by reference to the drawing attached to this specification. The single figure or the drawing shows, in diagram form, a cross section of a filter, oi. a type commonly used, one form of which is more elaborately described in U. S. Patent No. 2,107,664 to W. P. Gee.

In the drawing, i denotes a rotary filter drum.-

covered with filtering medium, such as cloth, rotating within a housing 2. The rotation is clockwise. The lower portion of the housing is filled with a feed slurry 3, comprising a mixture of precipitated wax, oil, and solvent. As the drum revolves the filter face passing through the feed slurry 3 picks up a wax cake, indicated by 4, the oil and solvent mix passing to the in- -terior of the drum and being disposed of from there. As the cake emerges from the liquid it is subjected to a drying period, and is then washed free of oil by awash solvent applied through sprays 5. After a further drying period, pressure is applied to the cake from within the drum, causing it to lift and break therefrom, and the broken cake is scraped from the drum by the blade 6. The sequence of these various operations is indicated by appropriately labeled sectors on the drum in the drawing. The arrangement of these operations and their appropriate duration may be varied widely according to the local operating conditions. The wash solvent applied through sprays! is normally the same solvent used in dewaxing, with or without, (usually substantially without), an additional amount of wax free oil.

waxing solvent may be used. For example in one form of the propane dewaxing process, the dewaxing solvent is liquefied propane and the wash solvent is liquid butane. When the term wash solvent is used herein, all such modifications' are contemplated.

Returning to the drawing, the wax cake removed by scraper is led into trough l and therein is crushed, conveyed, and removed by scroll conveyor 8. A very serious difliculty en-- countered in the operation of such filters is the tendency for the wax to build up and bridge over the'opening of the trough I, out of reach 01 the conveyor I as indicated by the dotted lines 9-9.. The formation of such a bridge will frequently render the filter inoperative in a short time because wax cannot be removed. Even when it is not this serious, the intermittent breakage of the bridge with the resultant delivery of large hard chunks of wax to the conveyor will hinder the operation of the conveyor, place undue shock loads upon the conveyor and its dewaxing mechanism, and frequently will cause breakage of the conveyor or conveyor drive and consequent shut down.

The object of this invention is to provide a method of operation wherein such apparatus may be run with assurance of easy and regular discharge of wax cake.

This operation is provided by the installation of a spray pipe ill in the space above the wax conveyor trough, through which spray it there is either continuously or intermittently introduced a spray of wash liquid at a temperature sufilcientiy high to partially melt or at least soften any bridged .cake and cause it to drop into the conveyor trough.

The spray pipe l0 may-be either a pipe extending throughout the length of the filter drum, with spray orifices along its under side, or, when the length voi! the filter drum is not great, spray In some instances a wash solvent of. different nature than the denozzles may be placed upon the ends of short pipes inserted through the housing from either end.

Usually the injection of hot wash solvent for,

a period of thirty seconds or so for every revolution of the drum (a single revolution taking about 6-8 minutes, usually), is sufllcient tokeep any cake slushed down into the conveyor trough and totally prevent bridging. Such intermittent operation may be controlled by a cycle timer, or

may be controlled by a simple valve tripping system actuated by drum rotation or by the drum drive.

The temperature of the slushing spray need not be unduly high, nor the quantity sprayed great in proportion to the amount of wax cake. A portion of the action is a physical washing of wax irom the scraper and into the trough. A portion of the action arises from softening of the wax. A portion of the action arises from the lubricating eiIect of the wash solvent and its tendency to prevent the wax from clinging to the scraper blade and trough walls.

Attempts have been made to avoid this difficulty by installing heating pipes within or adjacent to the trough. These, while effective,- complicate the operation, particularly with propane solvent in that the localized application of heat suificient to be eilective unduly vaporized what solvent may be in communication with the heater and increases the solvent vapor recovery load of the system. With this method, a suificient amount of heat maybe applied, distributed over a sufiicient area, so that no extensive vaporization of either wash solvent or dewaxing solvent is experienced.

2,2es,ves

closed continuous filter which comprises the steps 01' forming and washing a wax filter cake upon a travelling surface within the filter chamber, dislodging said cake and scraping it into a mechanical conveyor and spraying said cake on said scraper and in said conveyor with wash liquid to facilitate the movement of the wax in the conveyor.

2. The method of removing wax from oil in a closed continuous filter comprising the steps of forming a'wax cake irom a feed slurry of precipitated wax, oil, and dewaxing solvent upon a filtering surface travelling within the filter chamber, applying wash-solvent to said wax cake while on said surface, dislodging and scraping the wax cake from said surface, mechanically conveying the wax cake from said filter chamber, and intermittently flushing wax ,cake from the scraper and chamber parts around said conveyor by spraying wash solvent on said parts.

3. The method of operating an enclosed rotary drum filter for removal oi oil from wax wherein -a filter cake is formed upon the drum surface while submerged in a ieed slurry and washed with wash solvent after emersion and is then dislodged from the drum surface, scraped therefrom, and removed from the drum housing by a mechanical conveyor, comprising iorcibly spraying wash solvent, for short periods distributed throughout the operating cycle, upon the scraper, conveyor trough, and adjacent chamber parts to facilitate removal of wax therefrom.

4. The method of claim 3 in which the wash solvent introduced to the wax removal operation is heated to a temperature higher than the temperatures oi the wax cake at point of removal and at point of wax cake washing.

WALTER E. WANNER. DAVID F. annsnsw. 

